Fluid design for well stimulation applications



Inn 3,545,546

APPLICATIONS 12 Claims, No Drawing.

11.8. C1. 166/305 Int. Cl. E21b 43/25 Field of Search 166/305, 274, 273, 275, 306, 263, 311, 312

References Cited UNITED STATES PATENTS 2,331,594 10/1943 Blair, Jr 252/855 8/1944 Blair, Jr., et a1 252/855 Inventors Appl. No.

Filed Patented Assignee Harry Surkalo Findlay, Ohio;

Marion 0. Son, Jr., Littleton, Colorado 812,366

April 1, 1969 Dec. 8, 1970 Marathon Oil Company Findlay, Ohio a corporation of Ohio FLUID DESIGN FOR WELL STIMULATION 2,369,831 2/1945 J Jones et a1. 252/855 3,126,952 3/1964 Jones 166/305UX 3,185,217 5/1965 Brooks, Jr., et a1 166/305X 3,354,953 1 1/1967 Morse 166/305UX 3,402,770 9/1968 Messenger. 166/305 3,467,188 9/1969 Gogarty 166/274 3,474,865 10/1969 Gogarty et al. 1661274 3,477,51 1 1 1/1969 Jones et al. 166/274 Primary Examiner-Stephen J. Novosad Attorneys-Joseph C. Herring, Richard C. Willson, Jr. and

Jack L. Hummel ABSTRACT; Stimulation of a permeable, oil-bearing subterranean formation is effected by designing a micellar dispersion to have a mobility at least about two times the mobility of the combination of water and oil connate to the reservoir, then injecting from about 0.1 to about 10 barrels per vertical foot of oil bearing formation of the micellar dispersion into the formation and then injecting drive water to displace the micellar dispersion out into the formation.

FLUID DESIGN FORWELL STIMULATION APPLICATIONS 3 BACKGROUND OF-THE INVENTION Basic design conceptsofstimulating wells is to design the stimulation fluid to have a mobility that is equal to or less than that of the connate fluids within the subterranean formation. This design concept permits the stimulation fluid to push out ahead of it the connate fluids and possibly rewet the reservoir rock to the desired oil .wetness or water wetness. However, the drive fluid which displaces the stimulation fluid has a high mobility since it is usually water or a low molecular weight hydrocarbon. Thus, a very unfavorable mobility control is effected at the juncture of the back portion of the stimulation fluid and the drive fluid; such may cause severe fingering and inefficient displacement of the stimulationagent out into the formation.

Applicants have discovered a novel design concept of stimulating injection wells with a micellar dispersion wherein the micellar dispersion is designed to have a mobility substantially greater than the combined mobility of the oil and water within the subterranean formation. The designed mobility of the micellar dispersion is preferably closer to the mobility of the drive water than to the mobility of the combination of connate fluids, i.e. connatewater and connate hydrocarbon. By

such a design concept, the drive fluid can more effectively displace the micellar dispersionout into the formation and accomplish stimulation oftl e permeable formation.

DESCRIPTION OF THE INVENTION defined in US. Pat. Nos. 3,254,714 and 3,275,075 to Gogarty et al. and 3,307,628 to Sena. The art recognizes the differences between micellar dispersion technology and emulsion technology, one of the'major differences being that the equilibrium of the micellar dispersion tends towards further dispersion of the internal phase whereas the equilibrium of an emulsion tends toward coalescence of the internal phase.

The micellar dispersion is composed of hydrocarbon, aqueous medium, and surfactant. Cosurfactant(s) and electrolyte(s) can optionally be incorporated within the micellar dispersion. Examples of volume amounts include from about 4 percent to about 60 percent or more of hydrocarbon, from about 20 percent or less toabout 90 percent of aqueous medium, at least about 4 percent surfactant, about 0.01 to about 20 percent cosurfactant (also identified as cosolubilizer and semipolar organic compound) and from about 0.001 to about 5 percent or more (weight percent based on aqueous medium) of electrolyte. Optionally, other components compatible with the micellar dispersion can be incorporated to impart desired characteristics to the micellar dispersion.

The micellar dispersion can be oil-extemal or water-external. A particularly useful dispersion is an oil-external micellar dispersion having the capability of a large uptake of water and exhibiting lower viscosities upon the addition of water.

Hydrocarbons useful with the micellar dispersion include crude oil, partially refined fractions of crude oil, refined fractions of crude oil, and like materials. Specific examples include crude column overheads, side cuts from crude columns, gas oils, kerosenes, heavy naphtha, naphthas, straight run gasoline, liquefied petroleum gases, propane, pentane, heptane, cyclohexane, aryl compounds, substituted aryl compounds, etc. Preferably,-th e hydrocarbon can be characteristic of the hydrocarbon connate to the particular formation being treated, i.e. the physical makeupof the hydrocarbon can be very similar to the physical makeup of the connate hydrocarbon. The unsulfonated hydrocarbon within petroleum sulfonate, e.g. unsulfonated gas-oil s, are also useful as the hydrocarbon.

The aqueous medium can be a soft water, a brine water, or a brackishwater, Where aqueous medium does contain ions, it is preferred that the ions are compatible with the ions in the connate water.

Surfactants useful with the micellar dispersion include anionic, nonionic, and cationic surfactants. Specific examples of surfactant include those found in US. Pat. No. 3,254,714. Other useful surfactants include Duponol WAQE (a 30 percent active sodium lauryl sulfate marketed by DuPont Chemical Corporation, Wilmington, Delaware), Energetic W-l00 (a polyoxyethylene alkyl phenol marketed by Armour Chemical Company, Chicago, Illinois), Triton X,-l00 (an alkylphenoxy polyethoxy ethanol marketed by Rohm & Haas, Philadelphia, Pennsylvania) and Arquad 12-50 (a 50 percent active dodecyl trimethyl ammonium chloride marketed by Armour Chemical Company, Chicago, Illinois), and like materials.

Preferably, the surfactant is a petroleum sulfonate, also known as alkyl aryl naphthenic sulfonate. A particularly useful sulfonate is one having an average equivalent weight within the range of from about 360- to about 520 and contains a monovalent cation, e.g. sodium or ammonium petroleum sulfonate. More preferably, the equivalent weight of the sulfonate can be 400 to about 450. In addition, the surfactant can be a combination of two or more surfactants, and can be a mixture of low, medium and high equivalent weight sulfonates having'an average equivalent weight within the above-indicated ranges.

Cosurfactants useful with the invention include alcohols, amino compounds, esters, ketones, aldehydes and like materials containing from one to about 20 or more carbon atoms. Preferably the surfactant contains from about three to about 16 carbon atoms, and specificexamples include isopropanol, nand isobutanol, amyl alcohols such as n-amyl alcohol, l and Z-hexanol, l-and 2 -octanol, decylalcohols, dodecylal cohols', alkaryl alcohols such as p-nonylphenol and alcoholic liquors such as fusel oil, and like materials, Preferably, the cosurfactant can be present in concentrations within the range of from about 0.1 to about 5 percent. Mixtures of two or more cosurfactants are useful as are two or more different cosurfactants within the same class ofcosurfactants, i.e. amyl and 1- hexanol and optionally p-nonyl phenol.

Electrolytes useful in the invention include inorganic salts, inorganic bases, inorganic acids, organic acids, organic bases, and organic salts. Preferably, the electrolyte is one compatible with the sands within the subterranean formation. Specific examples of electrolytes include sodium hydroxide, sodium chloride, sodium sulfate, hydrochloric acid, sulfuric acid, and those electrolytes taught in US. Pat. Nos. 3,330,343 to Tosch 'et al. and 3,297,084 to Gogarty et al. The electrolytes can be the salts or ions within the aqueous medium, ie within the brine or brackish waters. The type and concentration of electrolyte will depend on the aqueous medium, surfactant, cosurfactant, hydrocarbon, and the reservoir conditions, including temperature of the reservoir! The mobility of the micellar dispersion should be substantially larger than that of the connate fluids, e.g. the mobility of the micellar dispersion can be at least about two times (200 percent) larger than the combined mobility of the water and oil within the subterranean formation. More preferably, the mobility of the micellar dispersion is at least 300 percent larger. than that of theconnate fluids. It can have a mobility approaching that of the mobility of the drive fluid, e.g. drive water or hydrocarbon drive fluid, which is injected behind the micellar dispersion.

Work resulting form well stimulation studies indicate that matched to the drive fluid mobility. For practical purposes, and for example only, this means that if the apparent viscosity contains data indicating results of the test:

of the c'onnate oil and water'is 30 cp., then the slug viscosity for stimulation should be about 10 cp. Such a design permits the drive water to more efficiently propagate the micellar the'flowof-fliiids.

Stimulation of. the formation can be obtained by injecting through'an injection means, e.g. a well in fluid communication dispersion out into the formation to stimulate the formation to with the formation frorn about 0.l less to aboutl or more barrelsof the "micellar dispersion per vertical foot of the formation. La iserfimb ln'ts can be injectedyhowever, it may be economically uriattractive forthe' results obtained. Preferably, fromabout l .toaboutfibarrels per vertical foot of the formaf tion'fto be stimulated of the micellar dispersion can be injected togive 'goodresults. Alfterthe micellar dispersion isinj ected into theTormatiori, sufficient drive fluid, e.g. drive water, is injected to displace the vdispersion out into the formation,

1 preferably out to ad i stance of at least about 7 to lSfeet.

The above date clearly indicates that the higher viscosity I stimulation fluids give a lower KRWF/KRWiratio whereas a The followingYexarnples are presented to teach specific working embodiments of the invention and should not be interpreted tolir'n'it in any way the scope of the invention.

' Further, all equivalents obvious to those skilled in the art are to be equated within the scope of the invention as identified within'the specification and appended claims. Unless otherwise specified, all percents are based on volume.

EXAMPLE 1 Core samples taken from the Curtis Field in Wyomingare flooded in: the followingm'anner. The cores are 1 inch in diameter and 3 inches long and are encapsulated in epoxy.

Five core samples are tested fortheir relative permeabilities to the. flow of water at residual oil, i.e. before stimulation'(thi s is referred to as KRWI). and thereafter the KRWF relative perrheability to flowof water after stimulation) is determined after the samples are treated by this invention. The viscosity of the stimulation fluid is indicated'in table I as is also the ratio of KRWF/KRWLIhe porevolume of the stimulation fluid injected is l.0 pore volumes of the micellar dispersion and the 5 pore volumeof the drive'water is 4.5 pore volumes. The miceli lar dispersion is samples A. B, and are composed of:

| 7 Percent l 1..... Sodium petroleum sullonate (Petronate HL, a trade- 6. 88 name of Sonneborn Chemical 00.. 300 Park Avenue 7 'South, New York, N.Y. 10010, having an average I moleeular'weight of about 440-470).

l 2 Sodium sultonate (Pyronate 50, a tradename of 4. 58 a Sonneborn' Chemical 00., having an average molecular weight of 350-375). 3. Kerosene 40.23 4. wagebrz'hiistilied water) containing 0.25 weight percent 47.

-o a 5..... Prlmaryamylalcohol 0. 72

f Ml. per 100 ml. of micellar dispersion.

Samples D and are flooded with the micellar dispersion having the above composition except there is present 0.95 ml. of primary amyl alcohol per 100 ml. of micellar dispersion slug.

The cores are flooded at 100 F. at constantflow rates. Table l f TABLE I Sample Number:

. lower viscosity, stimulation fluid gives a higherratio, thus an improvement in stimulation.

EXAMPLE 2 Core samples (from Oregon Basin, Wyoming) 1 inch in diameter by 3 inches long aree'ncapsulated' in epoxyr-jlhel procedure of example 1 is repeated except the amount of the primary amyl alcohol is adjusted in the micellar dispersion: to"

give the indicated viscosi ties outlined in table II. Table II indicates theresults obtained.

TABLE ir Sample Number:

EXAMPLES Cores'amples taken from the Send in Wyoming are tested. The samples are l inch in diameter and 3 inches long and areeneapsulatedin epoxy and are treated asdes'cribedin" example 1. indicated viscositiesof the micellar. dispersion are: obtained byadjusting the primary amyl alcohol within the micellar dispersion. Table lll indicatesthdt better stimulation is obtained by matching the mobility ofthe. micellar dispersion closer to the vater than that of theconnatefluids in the core:

. TABLE ITI Viscosity of stim- KRWF/KRWI ulation fluid at Sample Number: K- 1.3 42

We claim: y l. A method of increasingthe injectivity index of a subterranean formation in communication with an injection means, comprising:

l. injecting through the,injection.rn eans from about 0.1 to about l0 barrels of a micellar-dispersion per vertical foot of formation to bestimulated wherein the micellar dispersion is characterized as having a mobility substantially larger -than that of the mobility of the connate fluids inthe lardispersion is at least about two times as large as the mobilityof the combination of .connate water and oil in the, formation to be stimulated.

7. The method of claim 1 wherein the mobility of the micelsubterranean formation; and, lar dispersion is at least about three times largerthan the com 2, injecting sufiiciem drive water to displace the micellar bined mobility of the connate fluids Within the Subterranean dispersion out into the formation to a distance of at least formationabout 7 to l5 feet in radius fromthe well bore.

8. The method of claim 1 wherein sufficient drive water is 5 The method f l 9 wherein the micellar dispersion in ected into the formation to displace the micellar dispersion is comprised of hydrocarbon surfactant, water, and cosurfac out to a radius of at least about 7 to feet. tam

The methfxl f "f f 11. The method of claim 10 wherein the micellar dispersion ranean formation n commun cation with an in ection means contains 616 cuolyt e comprising: l0

12. The method of -claim 9 wherein the mobility of the micellar dispersion is closer to the mobility of the drive water than the mobility of the connate fluids within the subterranean formation.

1. injecting through the injection means into the formation from about 0.1 toabout l0 barrels per vertical foot of hydrocarbon-bearing formation of a micellar dispersion wherein the micellar dispersion has a mobility about two times larger than the mobility of the connate fluids in the 15 

